As far as he could fast travel during the previous missions without any problems, the location. [The Foundry] needs to be left on foot. Right now you're beginning of the largest area where there used to be the Custodian and you need to choose tunnels leading Northwards (the above screenshot).
After you get to the chamber, whose door was locked earlier, make use of the Northern passage you ignored before (the above screenshot), which is a series of narrow corridors. Their exploration is concerned with grabbing onto several interactive ledges, but this shouldn't pose any problem. The corridors will take you to the oval room of the foundry known to you perfectly.
Go North, and after you leave the foundry, you reach . [Tri-Stone] again. Pass over the large bridge that at the very beginning of the task was created by the keeper and use the passage leading up to the [Forge Lands] location.
Pass through the forge and moved to the northern part of the location. [Tri-Stone]. On your way there, you'd better meet with Muria the shaman and replenish your potions, although it's only optional. Proceed northwards and reach the exit from Tri-Stone (the above screenshot).
The last part of your journey is a journey to the [Stonefather's Vale] location, which is a large meadow located to the Northern part of [Tri-Stone]. Watch the cut scene, after you reach your destination. And you will learn that you are up for a battle with another Boss.